Udenafil is a drug used in urology to treat erectile dysfunction. It belongs to a class of drugs called PDE5 inhibitor, which many other erectile dysfunction drugs such as sildenafil, tadalafil, and vardenafil also belong to. It was developed by Dong-A Pharmaceutical Co., Ltd. and is marketed under the trade name Zydena. With a T max of 1.0-1.5 h and a T 1/2 of 11-13 h (a relatively rapid onset and a long duration of action), both on-demand and once-daily use of udenafil have been reported. Typical doses are 100 and 200 mg. Udenafil is available in Korea, Russia, and Philippines; in the United States, it is not approved for use U.S. Food and Drug Administration.